THE MASTERY OF THE AIR 239 
greatly increases their safety, their chances of 
getting food, their possibilities of trekking 
and migrating, and their opportunities—so 
plain in the wasp’s hanging nest—of laying 
their eggs or nurturing their young ones in 
places of comparative security, far from the 
ground, where danger always lurks. 
The second part of the answer is that insects 
have an extraordinarily successful make-up. 
Thus they have met the difficulty of captur- 
ing oxygen by developing a system of branch- 
ing air-tubes (trachee@), carrying oxygen to 
every hole and corner of the body. The per- 
fect aeration is part of the secret of the in- 
sect’s intense activity and success. The blood 
never becomes impure. Moreover, the beat- 
ing of the wings helps to drive the used air 
out, letting fresh air in. Just as in birds, 
which are also very successful, the flying helps 
the breathing. 
The third reason for the great success of 
insects is to be found in their remarkable de- 
velopment of instinctive behaviour. Along a 
line which is quite different from intelligence, 
they have been able to acquire a repertory of 
ready-made tricks, an inborn ability to do 
effective things right away without learning. 
